The effect of zinc-neutralized sulfonated EPDM (Zn-SEPDM) on the compatibility and the crystallizing behavior of isotactic polypropylene (IPP), and also the morphology of the blend were studied through WAXD, DSC, TEM, and mechanical properties test. The results show that addition of Zn-SEPDM decreases both the melting point and the crystallizing temperature of IPP. The widths at half-height of the melting peak and the crystallizing peak become narrower; the d-spacings of the crystal planes are unchanged, revealing the existence of interactions between Zn-SEPDM and the amorphous region of IPP. The higher the sulfonation level, the smaller the average distances across the IPP phase and the EPDM phase. As Zn-SEPDM content exceeds 20%, Zn-SEPDM in the blend becomes continuous and an abrupt change in impact strength is incurred therefrom. Owing to the incorporation of ionic groups into EPDM, the strong interactions between the chains make both the impact and the tensile strength of IPP remarkably higher.